For the first method make sure you don't mess up the link section at the bottom! The spaces have to be exactly like they are generated and there always have to be at least one empty line between your text and the link section. I never had problems using external images. I never tried < img src="" /> yet but i guess it should work as well...

At the moment i use only my public folder in my dropbox. It's the only (free) storage that doesn't get deleted after a few month ;) If you have dropbox just copy the image (or whatever) into the public folder, right-click it and select "copy public link" in the dropbox menu.